Decompression device for an internal combustion engine



Sept. 19, 1957 P. FARNY ETAL DECOMPRESSION DEVICE FOR AN INTERNAL COMBUSTION ENGINE Filed Oct. 21, 1965 5 Sheets-Sheet 1 Sept. 19 1967 FARNY ETAL I 3,342,169

DECOMPRESSIO N DEVICE FOR AN INTERNAL COMBUSTION ENGINE Filed Oct. 21, 1965 5 Sheets-Sheet 2 Fig.2

17 24 ,8 E -1 .1 I T 2s '3 16 'Y J 67 i i 2 1/ Sept. 19, 1967 P. FARNY ETAL 3,342,169

DECOMPRESSION DEVICE FOR AN INTERNAL comsusrxou ENGINE Filed Oct. 21, 1965 5 Sheets-Sheet 5 United States Patent once 3,342,169 Patented Sept. 19, 167

F ,3 Claims. (Cl. 123-182) ABSTRACT OF THE DISCLGSURE A decompression device for internal combustion engines of the class in which the compression is relieved by lifting one of the valves of the engine from its seat by a member to be placed in action before starting of the engine. The compression is restored automatically after a number of engine revolutions by a mechanism consisting substantially of a toothed wheel, a cam and a pawl which latter is put in motion by the valve push rods of the engine. During this restoration of compression the pawl engages the toothed wheel and returns it into a position in which the lifting member comes out of contact of the valve so that compression is restored in the engine. The pawl consists of an elongated member arranged substantially parallel with respect to the push rods and loosely inserted into the lifting member.

The invention relates to a decompression device for an internal combustion engine, and more particularly to an engine which is valve-controlled by means of pushrods.

According to the invention, there is provided in such an engine a decompression cam which can assume an ac tive decompression position and an inactive decompression position. The cam is provided with a driver wheel having teeth which are in driving connection with a driver which is associated with a reciprocating pushrod such that movement in one direction of the pushrod causes the driver to engage the teeth of the driver wheel and turn it, and the cam therewith, stepwise from the active decompression position to the inactive decompression position, Whereas upon movement of the pushrod in the other direction the driver becomes disengaged from the teeth of the driver wheel.

It is a first object of the invention to provide such a decompression device which is of simpleconstruction and is economical to manufacture.

Another object of the invention is to provide a decompression device which has minimum space requirements and which can be assembled in numerous advantageous positions.

Another object of the invention is to provide a decompression device which has great reliability of operation.

According to the invention, the above objects for a decompression device are obtained by an arrangement wherein a decompression cam acts on a lifting member which is guided in a recess in a housing and is arranged approximately parallel to a pushrod, said cam comprising a plate which abuts against a collar of a first pushrod when the decompression cam is in the active decompression position and in so doing holds the first pushrod in a position in which the associated valve is lifted away from its seat, said device further comprising a driver of substantially cylindrical form which is inserted loosely in a bore in the plate and is arranged approximately parallel to one of the pushrods and acts with a first end face on a collar of the second pushrod and with a second end face on one of the teeth of the driver wheel when the device is in the active decompression position.

The desired simplification is achieved due to the fact that the lifting member and driver are simple parts which are fitted freely in one another. This enables simple manufacture especially since no precise fits are required.

The desired reduction in space requirement is achieved by the approximate parallel arrangement of the lifting pin and driver relative to the pushrods, whereby an elongated construction is obtained which can be arranged satisfactorily in the pushrod space of an internal combustion engine, for example, in a pushrod sleeve surrounding two pushrods.

Reliability in operation is achieved by virtue of the construction wherein the driver is a substantially cylindrical part subjected to compressive stress which can be hardened in simple manner and which due to these features does not exhibit any wear or deformation even when frequently used.

The driver is made to disengage from the teeth of the driver wheel in a simple and therefore economical manner by providing the driver with a central collar which is urged against the side of the plate facing towards the driver wheel by a compression spring which is fitted over the driver, one end of said spring bearing on the side of the plate remote from the driver wheel whereas the other end of the spring bears on a holding collar situated in the vicinity of the first end face. By means of the compression spring, the driver is at the same time also brought back to its initial position, which further serves to achieve the desired simplification. Another substantial improvement in operating reliability is achieved by the fact that the first end face of the driver does not contact the collar of the second pushrod when the device is in the inactive decompression position. As a result of this feature, the driver operates only as long as the device is in operation, which prolongs the life of this part. Manufacturing costs are reduced by the fact that the compression cam is formed by the provision of a flat portion on one side of a shaft.

The collar of the first and second pushrods is conveniently adjustable in axial position therealong. This makes it unnecessary to observe excessively close tolerences.

The decompression cam is also conveniently arranged in the vicinity of the valve tappet. In this way it ispossible to arrange the decompression cam in a wall portion of the tappet guide or of the crankcase without any special constructional requirements.

An embodiment of the invention is illustrated in the attached drawings, wherein:

FIGURE 1 is a sectional view of an embodiment of the device according to the invention taken on the line II of FIGURE 3 in the active decompression position;

FIGURE 2 shows the device of FIG. 1 in the inactive decompression position; and

FIGURE 3 is a sectional view taken along the line III-III of FIGURE 1. i

In the drawing there is shown a tappet 1 which operates an exhaust valve (not shown) by means of an exhaust valve pushrod 2 which has been referred to hereinbefore as the second pushrod. The valve is operated by the pushrod in the usual way through the agency of a valve rocker (not shown). In front of the pushrod 2, in relation to the plane of the drawing, there is situated an inlet valve pushrod 3 (FIGURE 3) which has been referred to hereinbefore as the first pushrod. The pushrod 3 operates the inlet valve (not shown) in the same way as in the case of the exhaust valve. In the vicinity of the tappet 1 there is arranged a decompression cam 4. The decompression cam 4 is formed by a flat portion on a shaft 5 at one side thereof. A tooth system on the shaft 5 forms a driver wheel 6 which has ten teeth 7 and a toothless portion 8. Cooperating with the decompression cam 4 is a lifting member 9 which has a plate 10 which in the position illustrated in FIGURE 1 abuts against a collar of the pushrod 3 which is formed by a nut 11 and a lock-nut 12 (FIGURE 3) and is therefore adjustable in axial position along the pushrod 3. The lifting pin 9 is guided in a recess 13 which is arranged in the housing 14. The cam 4 thus serves in the active decompression position to hold the lifting member 9 and the pushrod 3 therewith in a raised position whereby the inlet valve will be opened. There is further provided in accordance with the invention means for stepwise moving the cam 4 from the active decompression position to the inactive decompression position for each successive stroke of the exhaust pushrod 2.

The means for stepwise moving the cam 4 comprises a driver 15 inserted loosely in a bore 16 of the plate It). The upper end face 17 of the driver 15, referred to hereinbefore as the first end face, acts on an axially adjustable collar 18 of the pushrod 2, while the lower end face 19 of the driver 15, referred to hereinbefore as the second end face, acts on the teeth 7 of the driver wheel 6. The driver 15 has a central collar 20 which is urged by a com pression spring 21 (constructed as a coil spring) against the underside 22 of the plate 10. The compression spring 21 bears at one end on the upper side 23 of the plate 10 and at its other end on the holding collar 24. The lifting member 9 is prevented from rotating about its axis by a cylindrical screw 26 and the member 9 is urged against the flat portion of the cam 4 by the compression spring 27.

The remainder of the device will be described in conjunction with the operation of the device which is as follows:

Before the internal combustion engine is started, shaft 5 and thus the earn 4 therewith are turned manually into the position shown in FIGURE 1 in a counterclockwise direction. This is effected by a lever 28 which is mounted on the shaft 5 and which in diesel engines can also be used to provide a larger delivery quantity from the injection pump for the purpose of improved starting. By means of the lifting member 9 the inlet valve is brought into the opened position, so that the internal combustion engine can easily turn over. At each second revolution, the reciprocating pushrod 2 moves in its longitudinal direction and in each downward stroke takes the driver 15 with it, this driver engaging one of the teeth 7 and turning the driver wheel 6 one tooth at a time in a counterclockwise direction. At each upward stroke of the pushrod 2, the driver 15 moves upwards under the action of spring 21. The conical portion of the pushrod 2 facilitates sliding movement of the pushrod 2 past the rear portion of the next tooth 7 coming into engagement. The driver 15 in so doing assumes a slightly inclined position in the bore 16. After twice as many revolutions as the driver wheel 6 has teeth (in this case after 20 revolutions) the internal combustion engine generally has an adequate rotational speed to start running reliably and the cam 4 has meanwhile reached the inactive decompression position shown in FIGURE 2, in which the plate 10 of the lifting member 9, which has moved downwards, no longer contacts the collar 11. Consequently, the inlet valve can close again normally and compression recommences. The introduced fuel is ignited and the internal combustion engine starts normal running. With the device in the position shown in FIGURE 2, the movement of the driver 15 ceases since the collar 18 no longer contacts the end face 17 of the driver.

From the above therefore, it is seen that there has been provided means for holding the inlet valve open for a prescribed period after which the inlet valve is automatically released for normal operation.

Numerous modifications and variations of the disclosed embodiment will become readily apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the attached claims.

What is claimed is:

1. In an internal combustion engine having an inlet and an exhaust valve and a reciprocating pushrod for operating a respective valve, the provision of a decompression device comprising cam means having an active decompression position and an inactive decompression position and supported for rotation between said positions, first means in engagement with said cam means for acting on the pushrod for the inlet valve to hold the same open in the active position of the cam means while being released from the pushrod for the inlet valve in the inactive position of the cam means, and second means operatively associated with the cam means for rotating the latter stepwise from the active to the inactive position thereof in dependence upon the strokes of the pushrod of the inlet valve, said carn means comprising a shaft of cylindrical shape having a flatted surface, said first means comprising a lifting member in contact with the shaft for contacting the cylindrical surface in the active position of the cam means and the flatted surface in the inactive position, means on said lifting member for engaging the pushrod for the inlet valve to raise the latter with the lifting member in contact with the cylindrical surface of the shaft and for releasing the pushrod of the inlet valve with the lifting member in contact with the flatted surface of the shaft, said second means including means activated by the contact of the lifting member with the cylindrical surface of the shaft and driven by the pushrod of the eX- haust valve to rotate the shaft stepwise.

2. In an engine as claimed in claim 1 wherein said means for rotating the shaft stepwise comprises a displaceable driver member coupled to said lifting member for being disposed in a position when the lifting member is in contact with the cylindrical surface of the shaft, such that the driver member is contacted and driven by the pushrod of the exhaust valve during one direction of stroke thereof, and a drive Wheel coupled for rotation with said shaft and driven stepwise by the driver member.

3. In an engine as claimed in claim 2 comprising a housing, said pushro ds, driver member and lifting member being supported in said housing in approximately parallel relation.

4. In an engine as claimed in claim 2 wherein said driver wheel has a toothed portion and a smooth portion, said driver member having an end for engaging successive teeth of the tooth portion to stepwise rotate the wheel until said end contacts the smooth portion of the wheel.

5. In an engine as claimed in claim 6 wherein said tooth portion and smooth portion are disposed relative to the flatted surface and the cylindrical surface of the shaft such that the lifting member contacts the flatted portion of the shaft when the end of the driving member contacts the smooth portion of the driver wheel.

6. In an engine as claimed in claim 5 wherein said driver wheel is integral with the shaft.

7. In an engine as claimed in claim 2 wherein said means on the lifting member for engaging the pushrod for the inlet valve comprises a plate secured to the lifting member, said plate having a bore in which the driver member is loosely accommodated.

8. In an engine as claimed in claim 7 wherein said means for rotating the shaft stepwise comprises a collar on said driver member located approximately midway thereof and a spring between said plate and that end of the driver which contacts the pushrod of the exhaust valve, said spring urging the collar on the driver member against the plate.

9. In an engine as claimed in claim 4 wherein said driver member comprises a conical portion at the end thereof which contacts said teeth of the driver wheel.

10. A decompression device for an internal combustion engine having at least two valves each actuated each by a pushrod, said device comprising: a decompression cam rotatable between an active decompression position and an inactive decompression position, a toothed driver wheel coupled to said cam for rotation therewith, driver means engageable with one of said pushrods for being driven thereby to engage the teeth of said wheel when moved by said pushrod in a first direction, said driver means disengaging from said teeth when moved opposite said first direction, said driver means turning said wheel step by step and the cam therewith from the active position of said cam to the inactive position thereof by engagement with successive teeth of said wheel, a lifting member operatively connected to said cam and movable substantially parallel to one of said pushrods, said lifting member having a fiat plate engaging a first of said pushrods with said cam in the active position and thereby lifting the valve associated with the pushrod into an unseated position; said driving means comprising an elongated driver member inserted loosely into a bore of said plate and arranged substantially parallel to one of said pushrods, said driver member having one end engaging a collar of the second of said pushrods and an opposite end engaging one of said teeth of said wheel when said cam is in active position.

11. A decompression device according to claim 10 comprising a spring mounted on the driver member, the driver member having a collar approximately midway of its length which is urged by the spring against that side of said plate which is nearest to said wheel; said spring having one end seated on that side of said plate which is furthest from said wheel and an opposite end which is seated in the vicinity of said one end of said driver member.

12. A decompression device according to claim 10, wherein said one end of said driver member is free of said collar of said second pnshrod with said cam in the inactive position.

13. A decompression device according to claim 10, wherein said cam is constituted by a one sided flat portion of a cylindrical shaft.

14. A decompression device according to claim 10, wherein said collars of said first and second pushrods are adjustable as to axial position along the respective pushrods.

15. A decompression device according to claim 10, wherein said cam is disposed in the vicinity of the cam followers of said pushrods.

References Cited FOREIGN PATENTS 5/ 1943 Germany. 8/1936 Great Britain. 

1. IN AN INTERNAL COMBUSTION ENGINE HAVING AN INLET AND AN EXHAUST VALVE AND A RECIPROCATING PUSHROD FOR OPERATING A RESPECTIVE VALVE, THE PROVISION OF A DECOMPRESSION DEVICE COMPRISING CAM MEANS HAVING AN ACTIVE DECOMPRESSION POSITION AND AN INACTIVE DECOMPRESSION POSITION AND SUPPORTED FOR ROTATION BETWEEN SAID POSITIONS, FIRST MEANS IN ENGAGEMENT WITH SAID CAM MEANS FOR ACTING ON THE PUSHROD FOR THE INLET VALVE TO HOLD THE SAME OPEN IN THE ACTIVE POSITION OF THE CAM MEANS WHILE BEING RELEASED FROM THE PUSHROD FOR THE INLET VALVE IN THE INACTIVE POSITION OF THE CAM MEANS, AND SECOND MEANS OPERATIVELY ASSOCIATED WITH THE CAM MEANS FOR ROTATING THE LATTER STEPWISE FROM THE ACTIVE TO THE INACTIVE POSITION THEREOF IN DEPENDENCE UPON THE STROKES OF THE PUSHROD OF THE INLET VALVE, SAID CAM MEANS COMPRISING A SHAFT OF CYLINDRICAL SHAPE HAVING A FLATTED SURFACE, SAID FIRST MEANS COMPRISING A LIFTING MEMBER IN CONTACT WITH THE SHAFT FOR CONTACTING THE CYLINDRICAL SURFACE IN THE ACTIVE POSITION OF THE CAM MEANS AND THE FLATTED SURFACE IN THE INACTIVE POSITION, MEANS ON SAID LIFTING MEMBER FOR ENGAGING THE PUSHROD FOR THE INLET VALVE TO RAISE THE LATTER WITH THE LIFTING MEMBER IN CONTACT WITH THE CYLINDRICAL SURFACE OF THE SHAFT AND FOR RELEASING THE PUSHROD OF THE INLET VALVE WITH THE LIFTING MEMBER IN CONTACT WITH THE FLATTED SURFACE OF THE SHAFT, SAID SECOND MEANS INCLUDING MEANS ACTIVATED BY THE CONTACT OF THE LIFTING MEMBER WITH THE CYLINDRICAL SURFACE OF THE SHAFT AND DRIVEN BY THE PUSHROD OF THE EXHAUST VALVE TO ROTATE THE SHAFT STEPWISE. 